fix combinedImage with file paths with spaces

[Pablo1107]

I got an uncaught error when trying to convert pdf to png. The pdf file path has some spaces and I figured that the command convert -append file with spaces.png "combinedImage.png" was the caused, and it was.

The solution involves adding the necessary espaced spaces in the command such that a line becomes convert -append file\ with\ spaces.png "combinedImage.png".

Please code review this PR, and merge if you consider it useful.